With United Airlines now the fourth major carrier to ground planes over the past month because of maintenance concerns, critics charge that the FAA is "too cozy" with the airlines it regulates. It's a situation, they say, that could eventually affect the safety of the flying public. As a result, critics are calling for a complete review and overhaul of the agency.

On Thursday, a major congressional hearing will feature the testimony of FAA whistle-blowers who allege that with the FAA's knowledge, Southwest Airlines continued to fly for up to 30 months airplanes that missed inspections.

"All eyes are on this now. We have a fundamental problem here," says Kevin Mitchell, chairman of the Business Travel Coalition, which represents corporate travel managers. "It's time for a giant step back for a top-down strategic review of the FAA."

The FAA denies that it has a "cozy" relationship. On Wednesday, it released a review of hundreds of airline maintenance records and found "an extraordinarily high rate" of airline compliance with its regulations. It says that the problems recently highlighted by whistle-blowers about Southwest Airlines, which prompted the review, were "aberrations."

"We would point out the unparalleled safety record as proof that the risk-based oversight system and voluntary reporting programs we have are producing results," says FAA spokesman Les Dorr. "The safety record we have today is not a result of chance, happenstance, or an accident."

Prior to 1996, the FAA had what was called a "fix and fly" method of aviation safety. When there was an accident or a problem was found, the FAA made sure that it was addressed on all planes. But the 1996 ValuJet crash, in which 110 people were killed in the Florida Everglades, changed that. Investigators cited lax FAA oversight as one cause of the crash. That prompted Congress to overhaul the agency, which until that time had had a dual charge of both regulating and promoting the aviation industry. After 1996, the FAA's sole responsibility was to regulate the airlines. At that time, the FAA also transformed its aviation safety regime, moving from a "fix and fly" system to one where airlines voluntarily reported problems in exchange for not being penalized. The FAA then used that information to predict potential problems and fix them before there could be an accident.

"When we find problems in the system, we certainly don't hesitate to act, and we've shown that many times in the past," says Mr. Dorr.

But some aviation experts and federal inspectors say that the pendulum in this cooperative relationship has swung too far, given the Southwest incident and maintenance problems also revealed at American, Delta, and United Airlines, which all resulted in planes being grounded.

At Thursday's hearing by the House Transportation and Infrastructure Committee, two FAA inspectors will allege that the FAA systematically failed to provide proper oversight of Southwest's maintenance operations over a number of years, according to a briefing by committee staff. The briefing also asserts that the problems with inadequate oversight may not be unique to Southwest.

In addition, the briefing also contends that FAA management works to ensure it doesn't "strain" relationships with airlines: "Many [FAA] inspectors allege that there is pressure from management not to identify too many problems with airlines, suggesting that there may be retribution or reassignment as a result."

Aviation experts, and even Committee Chairman James Oberstar (D), who is one of the industry's leading critics, say the aviation system is still safe. But Representative Oberstar says that to ensure this safety record continues, the FAA needs to change the way it's doing business. "We need a change of attitudes at the highest levels," he said on Tuesday, according to the Associated Press.

Aviation analysts draw similar conclusions. "It's obviously disconcerting to the traveling public that the FAA may not be doing its job as diligently as it should, at least in the light of some whistle-blowers," says Robert Mann, an aviation consultant with R.W. Mann & Co. in Port Washington, N.Y. "But I think the majority of this is going to be determined to be not substantive maintenance problems but rather paperwork issues."

The good news, says aviation expert Clint Oster at Indiana University in Bloomington, is that this is not happening in "the wake of airplanes falling out of the skies. Professor Oster applauds the recent decisions by American and Delta to ground some planes for further inspections, even if it was done as a result of a whistle-blower drawing attention to perceived problems within the FAA.

"These are precautionary moves," he says. "They're taking a proactive approach to something that's been in the back of industry people's minds for a while. That's a good thing."